Muscle Spindles/GTO neurophysiology

2 main sensory receptors

muscle spindles and golgi tendon organs

muscle spindles sense change in

length

GTOs sense change in

mm tension/force when its lengthened/shortned

where are GTOs located

between tendon and mm very small

main functions of MS and GTOs

proprioceptions

muscle spindles are ____ to extrafusal muscle fibers

parallel

GTO is in ___ to extrafusal muscle fibers

series

Extrafusal muscle fibers

-regular muscle fibers

-include slow (type 1) and fast (type IIa and b)

muscle spindles are

a complex intrafusal sense organ

-has 2 types

length of muscle spindles

4-10 mm in length

2 types of intrafusal muscle fibers for MS

nuclear bag and chain

nuclear bag

large diameter, clusted, central nuclei

2 subtypes of nuclear bags

static vs dynamic

nuclear chain

smaller diameter, mroe nuclei spread out, elongated

how many bags for each chain

1 chain:2 bags

2 types of Ia's

phasic and tonic

Ia phasics arise from

dynamic nuclear bag fibers

Ia tonics arise from

nuclear chain fibers

IIs arise from

flower spray receptors on the polar ends of the muscle spindles

Ia phasics afferents sense

BOTH the rate of muscle lengthening rate and muscle length changes

Ia tonics afferents sense

muscle length changes

BOTH Ia phasics and tonics are (3)

1)primary annulospiral receptors

2)facilitatory to agonists

3)inhibitory to antagonist

Ib afferents arise from

GTOs (encapsulated sense organs located in tendons)

-bring tension info up to brain

structure of GTOs

braided around neurons, 1mm long and 0.1 mm diameter

GTO's with contraction/stretching

pulls on GTOs and excited Ib afferents that synapses onto Ib inhibitory interneurons (connect to 15-20 muscle fibers)

basis/ mechanism for cross fiber massage at musculotendinous junction

direct pressure to GTO

-one of main mechanisms for contract-relax and hold-relax (could also be MS)

II afferents with alpha MN efferents cause

flexion on ipsilateral side and extension on contralateral side